The crown closure has been in existence since 1892 and is still the closure of choice for use on glass bottles, owing to its simplicity and effectiveness.
The crown closure, however, is not ideally suited to modern lightweight plastic or aluminium bottles because the bottle must be manufactured to the similar dimensions, in terms of thickness or strength, as a glass bottle to allow it to withstand the pressures and forces associated with the application of the closure, which is forced down and crimped around the top lip of the bottle. The standard screw closure has two main short comings in that the bottle must provide a tall and relatively heavy, in terms of material usage, thread form for retention of the closure, which reduces the opportunities to remove material, and hence weight, from the bottle. Particularly in the case of beer, the air volume entrapped in a screw closure, with its longer skirt length relative to a crown closure, has a detrimental effect on the keeping quality of the beer, because it is preferable to keep the levels of oxygen in contact with the product to a minimum.
Containers for fluids, in particular liquids, are commonly manufactured from aluminium, or a thermoplastic polymer resin such as polyethylene terephthalate [poly(ethylene terephthalate) or PET]. PET is often chosen in the manufacture of liquid containers, for its lightweight characteristic, high degree of impact resistance, and tensile strength. PET containers, especially bottles for liquids, are formed using two basic moulding methods, one-step or two-step.
In the two-step method, a first machine injection moulds a preform having a neck and a body. The neck of the preform has threads for applying a threaded screw cap, which threads are moulded into place in situ. The body of the preform is significantly thicker, because it is inflated into its final shape in the second step. In this step, the body of the preform is rapidly heated to high temperature, typically 95-115° C., and then stretched in the axial direction and inflated against a two-part mould to form the final shape of the bottle.
In the one-step method, the entire process from raw material to finished container is conducted within one machine, making it especially suitable for moulding non-standard shapes (custom moulding).
Bottles formed by either moulding method find utility in the food industry as containers for liquids such as carbonated drinks. The threads provided at the neck of the preform can, however, comprise a substantial weight, typically approximately 8-10% of the overall weight of the bottle.
Accordingly, it is an object of the present invention to provide a closure, which circumvents at least some of the shortcomings associated with the state of the art.